1. Field of the Invention
The present invention relates to an image printing apparatus such as a copying machine, printer, or facsimile apparatus, which forms a toner image by electrophotography and has a fixing unit which fixes the toner image on a paper sheet by applying pressure and heat.
2. Description of the Prior Art
An image printing apparatus based on electrophotography has a fixing unit which pressurizes and heats a paper sheet carrying a toner image while conveying the paper sheet by a pair of rollers to fix the toner image on the paper sheet. A heating roller used for this fixing unit incorporates a heater, and is heated when the heater is energized. The surface temperature of this heating roller is monitored by a temperature sensor. The heating roller is heated up to a predetermined temperature suitable for fixing operation on the basis of the obtained temperature information. Thereafter, the roller is maintained at the predetermined temperature by controlling power to be applied to the heater.
It generally takes several ten seconds to several minutes for the temperature of a heating roller to rise, upon energization of the heater, from room temperature to a temperature suitable for fixing operation. This period of time has been the wait time between the instant at which the power supply of an image printing apparatus is turned on and the instant at which the apparatus is set in an operable condition.
Recently, in order to perform control in accordance with an improvement in the function of an image printing apparatus, the control section of the apparatus body is formed by a computer system having a microcomputer as a main component. When the input power supply of the image printing apparatus is turned on, a power supply for supplying constant-voltage power to the control section is turned on. The control section then outputs a necessary reset signal to download a program stored in the memory of the control section into an area for the execution of the program by a small program loader called IPL or bootstrap. Starting the execution of this program will start predetermined control operation. An increase in program size, however, increases the download time described above. As a consequence, it takes much time to start energization control on the fixing unit. That is, for the user, this further increases the wait time between the instant at which the input power supply of the image printing apparatus is turned on and the instant at which the apparatus is set in an operable condition.
In order to solve this problem, a method of preventing an increase in wait time has also been proposed, which achieve this purpose by storing a fixing unit control program in a memory different from a memory in which a program is stored, and executing the fixing unit control program during downloading of the program (see, for example, Japanese Unexamined Patent Publication No. 2000-132042, p. 2, lines 2–14).
However, permission/inhibition of energization for heating the fixing unit poses problems not only when the input power supply of the image printing apparatus is turned on but also in, for example, a manufacturing process in a factory and technical services on the market. In other words, it is not necessarily good to keep the heater energized regardless of the control unit which controls the image printing apparatus body.